In general, when cells capable of proliferating three-dimensionally in vivo are cultured three-dimensionally, as a scaffold for the cells, for example, a collagen gel has been known. However, the collagen gel has a disadvantage that its application is limited by an animal or the like serving as a supplying source for the material.
Also, as a scaffold for the cells, a gel comprising peptides has been known (see, for example, Patent Publication 1 and Patent Publication 2). However, the gels disclosed in the Patent Publications 1 and 2 have a disadvantage that complicated procedures are required upon use.    Patent Publication 1: U.S. Pat. No. 5,670,483    Patent Publication 2: U.S. Pat. No. 5,955,343